Sustained-release preparations containing pharmaceutical active ingredients are attracting attention as highly useful preparations capable of controlling blood concentrations of pharmacologically active ingredients and sustaining pharmacological effects. In the past, water-soluble polymers that form a gel by contact with water were used as such sustained-release preparations, and considerable research has been conducted on sustained-release preparations that sustain the release of a drug from a preparation (matrix type sustained-release preparations).
The following lists examples of such matrix type sustained-release preparations.
(a) Patent Document 1 describes a process for preparing a formulated preparation having a prolonged controlled action, comprising the steps of: mixing a dry support composed of 80 to 95% hydroxypropyl methyl cellulose (HPMC) and 20 to 5% hydroxypropyl cellulose (HPC), drying the support to a moisture content of 1% or less, forming a dry formulated preparation by mixing a therapeutically effective amount of a therapeutic agent into the dry support, and compressing the dry formulated preparation into a prescribed shape; wherein, the HPMC and the HPC have a viscosity within the range of 50 to 25000 centipoise (cps) at 20° C. for a 2% aqueous solution.(b) Patent Document 2 describes a long-acting tablet comprising: fine particles of HPC, of which at least 50% by mass are able to pass through a 100 mesh screen, and HPMC having a hydroxypropoxy group content of 4 to 12%, methoxy group content of 19 to 30%, and viscosity in a 2% aqueous solution of 400 to 100,000 cps.(c) Patent Document 3 describes a sustained-release preparation in the form of a cisapride oral sustained-release composition comprising: approximately 9% by mass of cisapride-(L)-tartrate, approximately 61% by mass of lactose, 5.5 to 18% HPMC, 5.5 to 18% HPC and approximately 6.5% by mass of a lubricant.(d) Patent Document 4 describes a method for enhancing the gel strength of a preparation by containing HPMC and HPC in the preparation. According to the invention of a method for enhancing gel strength as described in this publication, it is described to the effect that gel strength is improved and a sustained-release preparation is obtained having superior sustained-release effects.(e) Patent Document 5 describes an active substance-containing preparation in the form of a compressed tablet comprising a support material in the form of a mixture high viscosity and low viscosity hydroxypropyl methyl cellulose.
However, in each of the preparation described in the above-mentioned publications, and in the case of tablets and the like in particular, since there are cases in which the drug does not completely elute from inside the preparation or conversely the elution speed of drug from inside the preparation is too rapid, there are cases in which the desired sustained-release effects are unable to be obtained, this requiring further improvement of the sustained-release preparation (sustained-release tablets).
In addition, Patent Document 6 describes an active substance-containing preparation in the form of solid particles obtained by finely mixing an active substance with a support material in the form of a water-soluble melt composed of (a) 10 to 90% by mass of a water-soluble polymer A having a viscosity of 1000 to 12000 cps and (b) 10 to 90% by mass of a water-soluble polymer B having a viscosity of 1 to 500 cps, and forming the melt into particles. In addition, HPMC and HPC are indicated as examples of water-soluble polymer A while HPC is indicated as an example of water-soluble polymer B in this publication.
However, since the art described in this publication involves the formation of solid particles after having heated and melted an active substance, water-soluble polymer A and water-soluble polymer B, problems are encountered particularly in the case of using an active substance that is unstable (changes easily) with respect to heat.    [Patent Document 1] Japanese Examined Patent Application, Second Publication No. H4-4301    [Patent Document 2] Japanese Patent (Granted) Publication No. 2134343    [Patent Document 3] Japanese Patent (Granted) Publication No. 3182423    [Patent Document 4] Japanese Unexamined Patent Application, First Publication No. 2004-217566    [Patent Document 5] Japanese Unexamined Patent Application, First Publication No. H7-53364    [Patent Document 6] Japanese Unexamined Patent Application, First Publication No. H6-172160